In recent years, the mobile communication field provides the system that multiplexes channels for transmitting different pieces of information at the same time and uses a radio line for transmission. An example of such system includes the W-CDMA system that is under discussion of 3GPP (Third Generation Partnership Project). The 3GPP specification additionally defines HSDPA (High Speed Downlink Packet Access) as a method of improving a rate of transmitting data from a base station to a mobile device (downlink). The HSDPA technology transmits reception quality information monitored on a mobile device and a reception determination result concerning reception data to the base station. This implements a downlink high-speed data transmission service that enables the adaptive modulation, the adaptive code rate, and the retransmission synthesis. To transmit the reception quality information and the reception determination result about reception data to the base station, a channel called HS-DPCCH (Dedicated Physical Control Channel for HS-DSCH) is transmitted in a code-multiplexing fashion with the conventional W-CDMA uplink. This code multiplexing increases a PAPR (Peak to Average Power Ratio), i.e., a ratio of transmission signal's peak power to average power, and degrades an ACLR (Adjacent Channel Leakage power Ratio). To improve the ACLR, it is necessary to improve linearity of a PA (Power Amplifier), increase the PA size, add a distortion compensation circuit, and the like (e.g., see JP-A No. 142959/2003). However, for example, this causes problems of increasing the power consumption and the circuit scale.
When the HS-DPCCH is currently available, a possible solution is to decrease the maximum transmission electric power at a fixed rate. However, decreasing the maximum transmission electric power inevitably limits the scope of HSDPA services. It is desirable to appropriately decrease the maximum transmission electric power depending on situations, not uniformly.
The present invention has been made in consideration of the foregoing. It is therefore an object of the present invention to provide a method and an apparatus for controlling transmission electric power capable of minimizing a decrease in the amount of maximum transmission electric power without degrading an adjacent channel leakage power ratio when code-multiplexing additional control information with data and main control information.